1. Field of the Invention
The present invention relates to a three beam-type projection apparatus, and more particularly to a three beam-type projection apparatus in which three projectors can be driven integrally so as to match three beam images on a screen and to focus the images on the screen simultaneously.
2. Description of the Prior Art
Generally, in a three beam splitting-type projection apparatus, three projectors corresponding to red, green and blue colors are placed at predetermined distances away from a screen. A projecting object is projected on a screen through each projector and the images obtained therefrom are overlapped to provide a viewer with a full color image.
In the three beam splitting-type projection apparatus, when the distances between the screen and the projectors and between the projectors themselves are not exactly adjusted, the images projected through the projectors are not matched.
The conventional three beam-type projection apparatus has three projectors for projecting red, green and blue color beams.
Each projector includes a light source such as xenon lamps, a spherical reflecting mirror for reflecting the light emitted backwards to the forward direction, a collimating lens for collimating the forwardly emitted and reflected light and for converting the collimated light into parallel light, a liquid crystal display (LCD) panel (or a slide film) as the projecting object, a projecting lens, etc.
Conventionally, the projectors are driven independently to adjust the reproduced image on a screen. That is, a first image is obtained on the screen by moving the focus of the image of one projector among the three projectors, vertically and horizontally. Then, a complete image is obtained by moving the remaining projectors vertically and horizontally.
In the three beam-type projection apparatus, in case the images projected on the screen through each projecting unit do not coincide or in case the focus of the image is not accurate due to inappropriate distances between the screen and each projecting unit, the projection direction and the projection angle should be adjusted by moving each projecting unit with respect to both the screen and the remaining projecting units to compensate for the deviation.
Accordingly, the operation is very complicated and inconvenient. In addition, since the adjusting operation is implemented manually while staring at the image reproduced on the screen, an accurate adjustment is very difficult if the operator is not an expert.
U.S. Pat. No. 5,125,733 (issued to Lee) discloses a stereoscopic projector for driving a pair of projecting lens holders integrally as a method for overcoming the abovementioned problems. In this patent, two projectors can be driven integrally and the adjustment of the image on the screen is very advantageous.
However, the apparatus utilizes only two projectors. Moreover, the apparatus is complicated and the manufacture thereof is not so advantageous.